Radiator is out, what can I do in the meantime?

I can think of one better!

While you have the rad out, take the timing cover off, and inspect the timing chain, if it's stretched, replace it with a cloys, then replace the water pump anyway if the system's drained. They're $25 for a new one. $30 for a new cloys timing set.

Also you can just blow the slant out with compressed air. That seems to move more junk out of it for me than flushing water through it. YOu'll also want to take the water pump off anyway to do that so you can blow it right into the water jacket. Then replace the 2" bypass hose from the water pump to the head.

There's tons you can do.

This is also a good time to degrease the front of the engine.